Re: [PATCH v20 2/2] dmaengine: tegra: Add tegra gpcdma driver

[Nathan Chancellor]

On Wed, Feb 23, 2022 at 03:49:09AM +0000, Akhil R wrote:
> > Hi Akhil,
> > 
> > On Mon, Feb 21, 2022 at 09:09:34PM +0530, Akhil R wrote:
> > > Adding GPC DMA controller driver for Tegra. The driver supports dma
> > > transfers between memory to memory, IO peripheral to memory and memory
> > > to IO peripheral.
> > >
> > > Co-developed-by: Pavan Kunapuli <pkunapuli@xxxxxxxxxx>
> > > Signed-off-by: Pavan Kunapuli <pkunapuli@xxxxxxxxxx>
> > > Co-developed-by: Rajesh Gumasta <rgumasta@xxxxxxxxxx>
> > > Signed-off-by: Rajesh Gumasta <rgumasta@xxxxxxxxxx>
> > > Signed-off-by: Akhil R <akhilrajeev@xxxxxxxxxx>
> > > Reviewed-by: Jon Hunter <jonathanh@xxxxxxxxxx>
> > > Reviewed-by: Dmitry Osipenko <digetx@xxxxxxxxx>
> > > ---
> > >  drivers/dma/Kconfig            |   11 +
> > >  drivers/dma/Makefile           |    1 +
> > >  drivers/dma/tegra186-gpc-dma.c | 1507
> > > ++++++++++++++++++++++++++++++++
> > >  3 files changed, 1519 insertions(+)
> > >  create mode 100644 drivers/dma/tegra186-gpc-dma.c
> > 
> > <snip>
> > 
> > > +static const struct __maybe_unused dev_pm_ops tegra_dma_dev_pm_ops =
> > > +{
> > 
> > The __maybe_unused cannot split the type ("struct dev_pm_ops") otherwise it
> > causes a clang warning:
> > 
> > https://lore.kernel.org/r/202202221207.lQ53BwKp-lkp@xxxxxxxxx/
> > 
> > static const struct dev_pm_ops tegra_dma_dev_pm_ops __maybe_unused = {
> > 
> > would look a litle better I think. However, is this attribute even needed? The
> > variable is unconditionally used below, so there should be no warning about it
> > being unused?
> > 
> > Cheers,
> > Nathan
> > 
> > > +     SET_SYSTEM_SLEEP_PM_OPS(tegra_dma_pm_suspend,
> > > +tegra_dma_pm_resume) };
> > > +
> > > +static struct platform_driver tegra_dma_driver = {
> > > +     .driver = {
> > > +             .name   = "tegra-gpcdma",
> > > +             .pm     = &tegra_dma_dev_pm_ops,
> > > +             .of_match_table = tegra_dma_of_match,
> > > +     },
> > > +     .probe          = tegra_dma_probe,
> > > +     .remove         = tegra_dma_remove,
> > > +};
> > > +
> > > +module_platform_driver(tegra_dma_driver);
> > > +
> > > +MODULE_DESCRIPTION("NVIDIA Tegra GPC DMA Controller driver");
> > > +MODULE_AUTHOR("Pavan Kunapuli <pkunapuli@xxxxxxxxxx>");
> > > +MODULE_AUTHOR("Rajesh Gumasta <rgumasta@xxxxxxxxxx>");
> > > +MODULE_LICENSE("GPL");
> > > --
> > > 2.17.1
> > >
> > >
> 
> Hi Nathan,
> 
> Thanks. Will update the same.
> 
> I am getting notification for the below warning also.
> 
> >> drivers/dma/tegra186-gpc-dma.c:898:53: warning: shift count >= width of type [-Wshift-count-overflow]
>                            FIELD_PREP(TEGRA_GPCDMA_HIGH_ADDR_DST_PTR, (dest >> 32));
> https://lore.kernel.org/all/202202230559.bLOEMEUh-lkp@xxxxxxxxx/
> 
> I suppose, this is because it is compiled against a different ARCH other than arm64.
> For arm64, the dma_addr_t is 64 bytes, and this warning does not occur.
> Could this be ignored for now? If not, could you suggest a fix, if possible?

I am not really familiar with the DMA API and dma_addr_t so I am not
sure about a proper fix.

You could cast dest to u64 to guarantee it is a type that can be shifted
by 32 but that might not be right for CONFIG_PHYS_ADDR_T_64BIT=n. If the
driver is not expected to run without CONFIG_PHYS_ADDR_T_64BIT, then
this is probably fine.

You could mark this driver 'depends on PHYS_ADDR_T_64BIT' if it cannot
run with CONFIG_ARCH_TEGRA=y + CONFIG_PHYS_ADDR_T_64BIT=n but I do not
see any other drivers that do that, which might mean that is not a
proper fix.

Please do not ignore the warning, as it will show up with ARCH=arm
allmodconfig, which has -Werror enabled.

Cheers,
Nathan